1. Field of the Invention
This invention relates to a method and system for anchoring refractory inside high temperature processing vessels, conduits and related equipment. Specifically, the invention describes a two-piece anchor suitable for spot welding or, in the alternative embodiment, stud welding.
2. Description of the Prior Art
In many chemical and petrochemical processing operations, processes occur inside vessels, conduits, cyclones, nozzle tips, air grids and related equipment having a high temperature and/or abrasive environment. To protect such equipment, a thin layer of erosion resistant refractory, usually castable concrete or plastics, is applied to the exposed surface. The common name for such protective material is simply xe2x80x9crefractoryxe2x80x9d.
Refractory commonly comes in two forms: pre-mixed and dry. In the pre-mixed form, the refractory comes in an approximately 50# 1xe2x80x2 cube. The refractory is sliced with a straight edge into 1xc2xdxe2x80x3 thick sections, and then pressed by hand into a support network of refractory anchors or mesh that is mounted on the surface to be protected. The refractory is further forced into the support structure for uniform distribution with a rubber-head pneumatic ramming gun, and then trowel finished flush with the support network structure.
In the dry form, the refractory is mixed in a large food-type mixer, and then applied and finished as with the pre-mixed form. After troweling of either form, the refractory is heat cured with a high temperature blower for final hardness.
The support structure provides a foundation structure to which the refractory anchors. The most common type of prior art is an interlocking honeycomb hexagonal steel grid known as xe2x80x9chexxe2x80x9d. This steel grid typically comes in 10xe2x80x2xc3x973xe2x80x2xc3x971xe2x80x3 sheets, have 2 xe2x85x9exe2x80x3 openings. The sheets are held together with clinches that clip through openings in the 1xe2x80x3 sides. The sheets are positioned against the surface to be protected, and are welded to that surface at the crotches of the mesh, typically at every other hex on every other row, for a 50% weld pattern.
Refractory is applied initially in new construction and is often replaced in repair (turnaround) jobs. In new construction and pre-turnaround jobs, the support anchors (such as hex) are usually welded on a horizontal lower surface for ease of positioning and welding. On a large vessel, this is accomplished by placing the vessel on support rollers that turn as each side is completed, such that all work is done on the floor surface of the vessel.
On a repair job, the old refractory is typically supported by honeycomb hex steel. Failure of the refractory is usually due to a localized buildup of by-products, such as coke, behind the refractory. This buildup creates pressure between the protected wall and the refractory, causing sections of the hex to break their welds away from the protected surface. The protection afforded by the refractory is then compromised, and the refractory must be replaced. To do so, the old hex section that failed is cut out on a perimeter, and the welds remaining within the failed section are broken away from the protected surface by xe2x80x9cribboning outxe2x80x9d the ribbons of hex with a chipping gun or an arc rod. The failed section of refractory/hex support is then removed. The remaining stubs on the vessel (or other protected) surface are ground down, new hex structure is welded to the protected surface, and new refractory applied.
Repairing existing hex with new hex is slow and difficult, requiring highly skilled craftsmen. As noted above, the old welds must be ground down for a smooth lay-down of the new hex. The new hex must be cut such that adequate support is provided in the patch area, without an excessive amount of new and old support being contiguous, thus preventing refractory in such areas. Hex is also difficult to work with on smaller and/or less planar surfaces, such as nozzle tips, cyclones, conduits, etc.
An alternative to hex in the prior art is found in a variety of independent anchors, each having their own benefits and limitations. U.S. Pat. No. 4,711,186 issued to Chen et al. discloses a refractory anchor having a curved xe2x80x9cXxe2x80x9d shape. Limitations include a solid weld and lower arms that restrict refractory flow during set-up, and incompatibility with stud welding. U.S. Pat. No. 4,753,053 issued to Heard discloses refractory curl anchors having ends transverse to a flat central member, to form a xe2x80x9cCxe2x80x9d. Limitations include the unilateral placement of the end anchoring means, which minimizes the amount of refractory where units are adjacent. In addition, the embodiments having asymmetrical structure do not afford uniform anchorage, and the one I-shaped embodiment affords poor coverage due to the transverse orientation of the end sections.
U. S. Pat. Nos. 4,479,337, 4,581,867 and 4,680,98 issued to Crowley disclose the Crowley S-anchor. Limitations include the single welding attachment point, which leads to heat induced strength failure. U.S. Pat. No. 4,660,343 issued to Raycher et al. discloses a Crowley S-anchor adapted for stud welding by cutting notches in the base of the anchor. Limitations include the requirement to affix two side plates (each being of 16 Gauge metal that is {fraction (1/16)}xe2x80x3 thick) to the weld base (also 16 Gauge) to achieve a sufficient width ({fraction (3/16)}xe2x80x3) to arrive at a 4:1 length:width ratio (xc2xexe2x80x3 length and {fraction (3/16)}xe2x80x3 width).
U.S. Pat. No. 4,651,487 issued to Nishikawa discloses tubular cylinder anchors having cutouts to allow refractory to migrate around the anchor. Limitations include inherent difficulties in welding around a small circle and limited flow into the cylinders.
It would therefore be useful improvement of the prior art for an independent refractory anchor that does not have the limitations of the prior art, including those described above.
Accordingly, the objectives of this invention are to provide, inter alia, a new and improved refractory anchor that:
is easily attached to a vessel wall;
is corrosion resistant;
can be adapted for stud welding;
allows uniform flow of refractory;
afford maximum refractory anchorage;
utilizes a symmetrical shape for uniform anchorage; and
is cost efficient.
These objectives are addressed by the structure and use of the inventive refractory anchor and method of use. Other objects of the invention will become apparent from time to time throughout the specification hereinafter disclosed.